L. Marrelli
A5054888636- Magnetic confinement fusion research
- Ionosphere and magnetosphere dynamics
- Superconducting Materials and Applications
- Particle accelerators and beam dynamics
- Plasma Diagnostics and Applications
- Laser-Plasma Interactions and Diagnostics
- Fusion materials and technologies
- Solar and Space Plasma Dynamics
- Nuclear Physics and Applications
- Physics of Superconductivity and Magnetism
- Nuclear reactor physics and engineering
- Particle Accelerators and Free-Electron Lasers
- Geomagnetism and Paleomagnetism Studies
- Semiconductor materials and devices
- Advanced MRI Techniques and Applications
- Laser-induced spectroscopy and plasma
- Magnetic Field Sensors Techniques
- Atomic and Molecular Physics
- Medical Imaging Techniques and Applications
- Particle Detector Development and Performance
- Atomic and Subatomic Physics Research
- Quantum chaos and dynamical systems
- Advancements in Semiconductor Devices and Circuit Design
- Quantum, superfluid, helium dynamics
- Electron and X-Ray Spectroscopy Techniques
National Agency for New Technologies, Energy and Sustainable Economic Development
2014-2024
University of Padua
1995-2024
Institute for the Science and Technology of Plasmas
2020
Max Planck Institute for Plasma Physics
2015-2017
Max Planck Society
2015-2017
Princeton Plasma Physics Laboratory
2006-2017
General Atomics (United States)
2017
Columbia University
2011-2017
University of California, San Diego
2017
United States Department of Energy
2017
The reversed field pinch (RFP) is a configuration for plasma magnetic confinement. It has been traditionally viewed as dominated by bath of MHD instabilities producing chaos and high energy transport. We report experimental results which go beyond this view. They show decrease the formation coherent helical structure in plasma, whose imaging temperature profile are provided first time. These quasi-single-helicity states observed both transiently stationary conditions. last case consistent...
Abstract This paper reviews the research on reversed field pinch (RFP) in last three decades. Substantial experimental and theoretical progress transformational changes have been achieved since review (Bodin 1990 Nucl. Fusion 30 1717–37). The experiments performed devices with different sizes capabilities. largest are RFX-mod Padova (Italy) MST Madison (USA). community includes also EXTRAP-T2R Sweden, RELAX Japan KTX China. Impressive improvements performance result of exploration two lines:...
We report the results of an experimental and theoretical international project dedicated to study quasi-single helicity (QSH) reversed field pinch (RFP) plasmas. The has involved several RFP devices numerical codes. It appears that QSH spectra are a robust feature common all experiments. Our expand reinforce evidence formation self-organized states with one dominant helical mode (Ohmic SH state) is approach complementary active control magnetic turbulence improve confinement in steady state RFP.
Stable operation with control on magnetohydrodynamic modes has been obtained in the modified reversed field experiment employing a set of 192 feedback controlled saddle coils. Improvements plasma temperature, confinement (twofold), and pulse length (threefold) and, as consequence magnetic fluctuation reduction, strong mitigation plasma-wall interaction mode locking are reported.Received 27 January 2006DOI:https://doi.org/10.1103/PhysRevLett.97.075001©2006 American Physical Society
Due to their discrete nature, a grid of active coils for the feedback control plasma instabilities produces an infinite sequence sideband harmonics in magnetic field. If sensors have same periodicity as coils, intelligent shell scheme (Bishop 1989 Plasma Phys. Control. Fusion 31 1179), aliasing sidebands determines systematic error on Fourier analysis measurements. Since relies raw measurements, it does not recognize effect. This is drawback field compensation and those perturbations that...
The loss of fast (i.e. suprathermal) ions from a magnetically confined fusion plasma due to the interaction with magnetohydrodynamic (MHD) instabilities has been experimentally characterized and interpreted by means numerical model. It is found that for special class instabilities, so-called neoclassical tearing modes, losses are increased modulated at same frequency mode. This new experimental finding explained as result drift islands formed energetic in particle phase space. An eventual...
The RFX-mod machine (Sonato et al 2003 Fusion Eng. Des. 66 161) recently achieved, for the first time in a reversed-field pinch, high plasma current up to 1.6 MA with good confinement. Magnetic feedback control of magnetohydrodynamic instabilities was essential reach goal. As is raised, spontaneously accesses new helical state, starting from turbulent multi-helical conditions. Together this raise, ratio between dominant and secondary mode amplitudes increases continuous way. This brings...
RFX-mod is a Reversed Field Pinch device that allowed performing experiments in regimes with plasma current up to 2 MA, thanks its MHD active control system. Experiments have shown improved performances are obtained when the resonant part of m = 1 spectrum one dominant tearing mode much higher than other secondary ones (quasi single helicity states). Tearing modes play crucial role determining energy and particle transport. Based on present understanding interplay between passive conductive...
Active feedback stabilization of multiple independent resistive wall modes is experimentally demonstrated in a reversed-field pinch plasma. A reproducible simultaneous suppression several nonresonant achieved. Coupling different due to the limited number coils observed agreement with theory. The RWMs also has an effect on tearing that are resonant central plasma, leading significant prolongation discharge pulse.
Reduction of core-resonant m=1 magnetic fluctuations and improved confinement in the Madison Symmetric Torus [Dexter et al., Fusion Technol. 19, 131 (1991)] reversed-field pinch have been routinely achieved through control surface poloidal electric field, but it is now known that has limited part by edge-resonant m=0 fluctuations. Now, refined field control, plus toroidal possible to reduce simultaneously This allowed high-energy runaway electrons, possibly indicative flux-surface...
The resistive wall mode (RWM) and neoclassical tearing (NTM) have been simultaneously suppressed in the DIII-D for durations of over 2 s at beta values 20% above no-wall limit with modest electron cyclotron current drive very low plasma rotation. achieved rotation was significantly lower than reported previously. However, this regime where stable operation is obtained, it not unconditionally guaranteed. Various MHD activities, such as edge localized modes (ELMs) fishbones, begin to couple...
Disruption-generated runaway electron (RE) beams represent a severe threat for tokamak plasma-facing components in high current devices like ITER, thus motivating the search of mitigation techniques. The application 3D fields might aid this purpose and recently was investigated also ASDEX Upgrade experiment by using internal active saddle coils (termed B-coils). Resonant magnetic perturbations (RMPs) with dominant toroidal mode number n = 1 have been applied B-coils, RE specific scenario,...
We describe plasma profiles evolution during pulsed poloidal current drive experiments performed with the RFX reversed field pinch device. With external of edge current, magnetic fluctuations are reduced suggesting a concomitant reduction spontaneous dynamo action. The electron temperature profile is seen to peak in core, consistently heat conductivity due substantial decrease MHD fluctuations. Our results also indicate that turbulence these fluctuations, which dominates transport core...
SXR cross-sectional distributions measured in the European reversed field pinch (RFP) experiment RFX by means of a tomographic diagnostic are described. Various reconstruction techniques have been compared. A correction technique to minimize systematic effect due non-identical thicknesses material filters has developed. number experimental situations explored, and study correlation between MHD properties plasma made. The analysis concentrates both on standard discharges recently discovered...
Magnetic field lines and the corresponding particle orbits are computed for a typical chaotic magnetic provided by magnetohydrodynamics numerical simulation of reversed-field pinch. The $m=1$ modes phase locked produce toroidally localized bulging plasma which increases transport. $m=0$ chaos implying poor confinement. However, they also allow formation islands induce transport barriers inside reversal surface.
RFX-mod is a reversed field pinch (RFP) experiment equipped with system that actively controls the magnetic boundary. In this paper we describe results of new control algorithm, clean mode (CMC), in which aliasing sideband harmonics generated by discrete saddle coils corrected real time. CMC operation leads to smoother (i.e. more axisymmetric) Tearing modes rotate (up 100 Hz) and partially unlock. Plasma–wall interaction diminishes due decrease non-axisymmetric shift plasma column. With...
A detailed knowledge of the interplay between MHD instabilities and energetic particles has been gained from direct measurements fast-ion losses (FILs). Time-resolved energy pitch angle FIL caused by neoclassical tearing modes (NTMs) toroidicity-induced Alfven eigenmodes (TAEs) have obtained using a scintillator based detector. The study due to TAEs revealed existence new core-localized fluctuation, Sierpes mode. mode is non-pure Alfvenic fluctuation which appears in acoustic branch,...
We define the safety factor $q$ for helical plasmas of experiment RFX-mod by accounting actual three-dimensional nature magnetic flux surfaces. Such a profile is not monotonic but goes through maximum located in vicinity electron transport barriers measured high resolution Thomson scattering diagnostic. Helical states with single axis obtained viscoresistive magnetohydrodynamic numerical simulations exhibit similar nonmonotonic profiles provided that final are preceded island phase, like experiment.
With the exploration of MA plasma current regime in up to 0.5 s long discharges, RFX-mod has opened new and very promising perspectives for reversed field pinch (RFP) magnetic configuration, made significant progress understanding improving confinement controlling stability. A big leap with respect previous knowledge expectations on RFP physics performance been by since last 2006 IAEA Fusion Energy Conference. self-organized helical equilibrium experimentally achieved (the Single Helical...
The hybrid scenario is a candidate for stationary high-fusion gain tokamak operation in ITER and DEMO. To obtain such performance, the energy confinement normalized pressure must be maximized, which requires operating near or above ideal MHD no-wall limits. New experimental findings show how these limits can affect operation. Even if hybrids are mainly limited by tearing modes, proximity to limit leads 3D field amplification that affects plasma profiles, e.g. rotation braking observed ASDEX...
Abstract The RFX-mod2 installation is planned to be completed by 2024 and the start of operations expected in 2025. high flexibility machine (already tested previous RFX-mod experiment) allows operation Reversed Field Pinch tokamak configuration as well ultra-low q pulses. In this work we present predictive analysis on transport, performances plasma control view first experimental campaigns.
This paper reports experimental results showing that coherent helical structures are formed in the reversed field pinch (RFP) self-organizing plasma core as a result of transitions to states where n-spectrum m=1 modes is dominated by single (1,nmax) geometrical helicity. These dubbed quasi-single helicity (QSH) states. Their magnetic and thermal properties measured reverse experiment (RFX) [G. Rostagni, Fusion Eng. Des. 25, 301 (1995)] device described. The present theoretical understanding...
Active feedback control of resistive wall modes (RWMs) has been demonstrated in the EXTRAP T2R reversed-field pinch experiment. The system includes a sensor consisting an array magnetic coils (measuring mode harmonics) and actuator saddle coil (producing harmonics). Closed-loop (feedback) experiments using digital controller based on real time Fourier transform data have studied for cases where gain was constant all harmonics (corresponding to intelligent-shell) could be set selected...
Optimization of machine operation, including plasma position control, density control and especially feedback on multiple magnetohydrodynamic modes, has led RFX-mod to operate reliably at 1.5 MA, the highest current ever achieved a reversed field pinch (RFP). At high low magnetic topology spontaneously self-organizes in an Ohmical helical symmetry, with new axis helically twisting around geometrical torus. The separatrix island disappears leaving wide symmetric thermal structure large...